1. Field of the Invention
This invention relates to electrical leads for transferring electrical power into and out of devices inside a cryostat, and more particularly to a multi-circuit cryostat power lead.
2. Background of the Invention
Commonly owned U.S. patent application Ser. No. 07/585,419 filed on Oct. 20, 1990 discloses a hybrid vapor cooled power lead for transferring power to and from devices inside a cryostat. Such power leads have application for instance in providing power to and withdrawing power from the magnets of the proposed superconducting supercollider now under development and for large electric power storage magnets. This hybrid power lead has an inner section with high temperature superconducting lead elements. That is, conductors which are superconducting at temperatures well above the 3 or 4 degrees Kelvin required for conventional superconducting materials. Thus, there is no joule heating in this section of the power lead. The outer section of the hybrid power lead incorporates normal conductors such as copper lead elements.
This power lead has a number of high temperature superconductor elements and copper elements all connected in parallel to form a single circuit, high current, lead. A flow of helium vapor from the cryostat is directed over the high temperature superconducting and normal conductor lead, elements by a tubular enclosure. In one embodiment of this earlier hybrid power lead, the tubular enclosure around the copper conductors includes an inner tube in which a secondary cryogen vapor such as nitrogen is introduced, and an outer tube forming an annulus with the inner tube through which the helium vapor from the high temperature superconducting section flows to provide additional cooling for removing the joule heating and conduction heating of the copper conductor section.
There are some applications where it is desirable to have multi-circuit power leads. For instance, the superconducting supercollider has a number of control magnets. While these magnets do not require the huge amounts of power of the main magnets, they still require sizeable power input. Each penetration of the cryostat in which the magnets are enclosed results in a heat loss. Significantly more energy is required to make up the cooling that is lost in a heat leak. Therefore, it is desirable to minimize the heat leaks attributable to penetrations of the cryostat as much as possible.